Experimental and Analytical Estimation of Loss Factors by the Power Input Method

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The Power Input Method (PIM) is used both experimentally and a nalytically to estimate the system loss factor for sandwich panels with various configurations of Constrained Layer Damping (CLD) treatments over a broad frequency range. The experimental power input method is applied to both uniformly and non -uniformly da mped structures. Results are compared with results from other experimental methods. A new analytical power input method is proposed for evaluating the loss factor of built -up structures, based on the finite element model with assigned properties of the con stituents. The new analytical power input method is evaluated by comparison with the commonly used Modal Strain Energy (MSE) method. Instead of making an approximate correction of the constant material properties, this analytical power input method directl y takes into account the frequency -dependent material properties of the viscoelastic material using the MSC/NASTRAN direct frequency response solution. Results of experimental and analytical methods are presented, compared and discussed. It is shown that: 1) all three currently available experimental methods yield consistent results, while the power input method gives damping estimation other than just at several discrete frequencies basically in the low frequency range; 2) both the analytical power input m ethod and the modal strain energy method yield consistent results with the experimental power input method. Furthermore, both experimental and analytical power input methods are used to investigate how loss factors change as the excitation position change. This shows another merit of the analytical power input method, because analytical modal methods cannot take into account the change of excitation position.